Automated system, and corresponding method, for testing electro-optic modules

ABSTRACT

An automated, computer-controlled system, and a corresponding method, for testing electro-optic modules, is disclosed.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention pertains to an automated system, and to a correspondingmethod, for testing electro-optic modules.

2. Description of the Related Art

Those engaged in the manufacture and use of communication systems, e.g.,systems for communicating voice, video and/or data, have becomeincreasingly interested in using fiber optic cables as transmissionmedia in such systems. This interest is stimulated by the fact that thepotential bandwidth (or information-carrying capacity) of optical fibersis extremely high. In addition, communication systems employing fiberoptic cables are resistant to electromagnetic interference, whichsometimes plagues systems employing electrical cables as transmissionmedia. Moreover, communication systems employing fiber optic cables areconsidered more secure than systems employing electrical cables becauseit is generally more difficult for unauthorized personnel to tap oraccess a fiber optic cable without being detected.

An exemplary communication system employing a fiber optic cable as atransmission medium is one which includes, for example, two or morecomputers, with each adjacent pair of computers being interconnected bya fiber optic cable which includes two optical fibers, i.e., a transmitoptical fiber and a receive optical fiber. Obviously, each computergenerates and receives information, i.e., data, in electrical form.Consequently, each computer is also provided with an electro-opticmodule, typically mounted on a printed circuit board or printed circuitcard of the computer, which converts the electrical signals generated bythe computer into optical signals, which are transmitted to the adjacentcomputer via the transmit optical fiber. In addition, the electro-opticmodule converts optical signals communicated to the computer via thereceive optical fiber into corresponding electrical signals.

An electro-optic module, of the type referred to above, necessarilyincludes an electro-optic transmitter and an electro-optic receiver.That is, such a module typically includes a housing containing atransmitter optical subassembly (TOSA), a receiver optical subassembly(ROSA) and a pinned ceramic substrate bearing a number of semiconductorintegrated circuit devices. Certain of these integrated circuit devicesperform transmitter-related functions (and are hereinafter denoted thetransmitter ICs) and certain of these integrated circuit devices performreceiver-related functions (and are hereinafter denoted the receiverICs). The TOSA, which is electrically connected to the transmitter ICs,includes an electro-optic transducer, such as a semiconductor laser or alight-emitting diode (LED), which serves to convert the digitalelectrical signals generated by the transmitter ICs into correspondingdigital optical signals. It is the combination of the TOSA andtransmitter ICs which constitutes the transmitter of the module.Similarly, the ROSA, which is electrically connected to the receiverICs, includes an electro-optic transducer, such as a PIN photodiode,which serves to convert received digital optical signals intocorresponding digital electrical signals communicated to the receiverICs. It is the combination of the ROSA and receiver ICs whichconstitutes the receiver of the module.

The electrical data communicated by a computer to its electro- opticmodule is typically communicated in parallel form, whereas thetransmitter of the electro-optic module is only capable of receivingelectrical data, and producing corresponding optical data, in serialform. Consequently, the printed circuit board or printed circuit card onwhich the module is mounted usually includes a so-called serializersemiconductor integrated circuit device, which serves to convertparallel electrical data into serial electrical data. Similarly, thereceiver of the electro-optic module is only capable of receivingoptical data in serial form, and of converting it into correspondingserial electrical data, whereas this electrical data is to becommunicated to the computer in parallel form. Therefore, the printedcircuit board or printed circuit card on which the module is mountedusually includes a so-called deserializer semiconductor integratedcircuit device, which serves to convert serial data into parallel data.

A communication system employing fiber optic cables and electro-opticmodules can only operate effectively if its components, including itselectro-optic modules, operate in conformity with correspondingoperating specifications. Therefore, it has become important to testelectro-optic modules to make sure that these modules conform to thesespecifications, and to detect and correct errors in manufacturingprocesses which lead to non-conformities in the modules.

The operating specifications, referred to above, typically imposelimitations on certain parameters which characterize the performance ofa transmitter and of a receiver of an electro-optic module. For example,the transmitter is usually characterized by parameters such astransmitter average power, transmitter rise/fall time, transmitterextinction ratio, transmitter duty cycle distortion and transmitter datadependent jitter, all of which parameters are defined below inconnection with the present invention. In addition, the receiver isusually characterized by parameters such as receiver sensitivity,receiver pulse width distortion, receiver signal detect threshold andreceiver signal detect assert/deassert times, which parameters are alsodefined below. Significantly, until the present invention, the testsdevised to measure these parameters have all been manual and havetherefore required an inordinate amount of time to perform. For example,if one were to manually measure all of the parameters listed above, thenthis would typically require several hours. As a consequence, it hasthus far been impractical and prohibitively expensive, for example, fora manufacturer of electro-optic modules to test each and everyelectro-optic module manufactured by him, or even a statisticallysignificant fraction of such modules, in order to weed out those whichfail to conform to the corresponding specification.

To illustrate the above point, it should be noted that in order tomeasure, for example, receiver sensitivity, using conventional manualtechniques, it is first necessary to manually determine thecorresponding eye pattern. That is, a digital electrical serial patterngenerator (a type of digital signal generator), having an internalclock, is electrically connected to a semiconductor laser or LED whichis optically connected to the receiver under test via an optical fiber.The output of the receiver is, in turn, electrically connected to adigital oscilloscope. In addition, the output of the internal clock ofthe serial pattern generator is electrically connected, through amanually adjustable time delay unit, to the same digital oscilloscope.The serial pattern generator is then used to transmit a pseudo-randomdigital electrical signal to the semiconductor laser or LED, at atransmission speed (bit rate) to be used in the correspondingcommunication system. The semiconductor laser or LED produces acorresponding pseudo-random digital optical signal, which iscommunicated to the receiver via the optical fiber. In addition, theresulting pseudo-random digital electrical signal generated by thereceiver is communicated to the digital oscilloscope, which is triggeredby the square -wave clock pulses generated by the internal clock of theserial pattern generator. The transmission speed (bit rate) of thesesquare wave pulses is, of course, the same as that of the pseudo-randomdigital electrical signal.

As each clock pulse triggers the digital oscilloscope, that portion ofthe pseudo-random digital electrical signal which is produced by thereceiver and is subsequent to the triggering pulse is displayed on theoscilloscope and superimposed on previously displayed portions. Byadjusting the oscilloscope to display only a segment of the superimposeddigital signals corresponding to the width of a single electrical pulse,a pattern of voltage crossings, like that shown in FIG. 1, is produced.This pattern, called an eye pattern, depicts the number of voltagechanges associated with the pseudo-random digital electrical signalproduced by the receiver. It should be noted that the width of the eyepattern is related to the time interval during which each pulse in thepseudo-random digital signal being produced by the receiver may besampled without error, i.e., the wider the eye pattern, the longer thetime interval, and vice versa. This is important in connection with thedeserializer semiconductor integrated circuit device mounted on theprinted circuit board or printed circuit card because this device istypically only capable of sampling the electrical pulses produced by thereceiver over a particular time interval and, to avoid errors, the widthof the eye pattern should be equal to or greater than this deserializertime interval.

When considering receiver sensitivity, it should be understood that thisterm denotes the average power of the weakest optical signal thereceiver can detect and maintain a specified bit error rate (BER). Thus,receiver sensitivity could, in principle be measured by adding a digitalelectrical serial pattern comparator to the apparatus described above,which comparator is capable of comparing the pseudo-random digitalelectrical signal produced by the receiver to that generated by theserial pattern generator, and counting the number of bits which are inerror, while varying optical power. That is, one could connect theelectrical output of the receiver to the serial pattern comparator,connect the electrical output of the internal clock of the serialpattern generator to the serial pattern comparator and manually adjustthe time delay unit to the setting corresponding to the center of theeye pattern. Then, at a specified average optical power of the laser OrLED, one could accumulate a sufficient number of bits and count thecorresponding number of bits which are in error. If the desired BER isnot achieved, one could then increase or decrease the optical power andrepeat the above procedure. However, if it is necessary to achieve a BERof, for example, 10**-12 or 10**-15 (as is now required in many computersystems), then one must necessarily accumulate at least 10**12 or 10**15bits, which could easily take hours or days.

To reduce the amount of time required to measure receiver sensitivity,it is conventionally assumed that the noise in the receiver is Gaussianin nature and, for a fixed temperature, is constant. As a consequence,it follows that a signal-to-noise parameter, Q, associated with thereceiver increases linearly with received average optical power, P(expressed) in milliwatts), where ##EQU1## Stated alternatively, itfollows that the log (base 10) of Q is linearly proportional-to P,expressed in decibels (dB), as depicted in FIG. 2. It also follows fromthe above assumptions, and it has been believed, that the slope of logQversus P (expressed in dB) is equal to 0.0946 dB**-1 for values of logQranging from about 0.677 to about 0.847. Moreover, it follows that BERis related to Q through the complementary error function, i.e., ##EQU2##Thus, if BER has been measured at a particular value of P, one can thencalculate the corresponding value of Q from Equation (2). Furthermore,with this one data point, one can then obtain a plot of logQ versus P(expressed in dB) by extrapolation, using the above-mentioned slope.

Conventionally, to save time, when manually measuring receiversensitivity, one uses the above-described apparatus to measure the BERcorresponding to a relatively low average optical power, P. Because P isrelatively low, it follows that the BER will be relatively high, e.g.,10**-8, and therefore it is only necessary to accumulate a relativelysmall number of bits, e.g., 10**8, which requires a relatively shortperiod of time. Using Equation (2), it is then conventional to calculatethe corresponding value of Q and, based upon the assumption that theslope of logQ versus P (in dB) is 0.0946 dB**-1, obtain a plot of logQversus P (in dB) for the receiver under test. To determine the powerlevel needed to achieve a desired BER, one then solves Equation (2) forthe corresponding value of Q. Using this value of Q, it is thenconventional to use the plot of logQ versus P (in dB) to determine thecorresponding value of P.

Using the time-saving procedure described above, a manual measurement ofreceiver sensitivity still requires about thirty (30) minutes.Unfortunately, this is far too long to permit each and everyelectro-optic module to be tested. In fact, this is far too long topermit even a statistically significant number of modules to be tested.

Thus, those engaged in the development and manufacture of fiber opticcommunication systems, in general, and of electro-optic modules, inparticular, have long sought, thus far without success, systems andmethods for testing electro-optic modules which require relatively shorttesting times.

SUMMARY OF THE INVENTION

The invention involves an automated, computer-controlled system, and acorresponding method, for testing electro-optic modules. This system iscapable of automatically measuring various parameters associated withthe transmitter and/or receiver of an electro-optic module. Theseparameters include transmitter average power, transmitter rise/falltime, transmitter extinction ratio, transmitter duty cycle distortionand transmitter data dependent jitter. These parameters also includereceiver sensitivity, receiver pulse width distortion, receiver signaldetect threshold and receiver signal detect assert/deassert times. Theautomated system is readily capable of measuring all of these parametersin no more than about three (3) minutes. As a consequence, it is nowpossible for a manufacturer of electro-optic modules to test each of hismanufactured modules, or a statistically significant number of modules,in a relatively short period of time, e.g., three (3) minutes, and at arelatively low cost.

BRIEF DESCRIPTION OF THE DRAWINGS(S)

The invention is described with reference to the accompanying drawings,where:

FIG. 1 is a photograph of an oscilloscope screen showing an eye patternassociated with the receiver of an electro-optic module;

FIG. 2 is a plot of log Q (on the left-hand vertical scale) and of BER(on the right-hand vertical scale) versus P (in dB), where the slope ofthis plot is based upon theory;

FIG. 3 is a schematic diagram of a preferred embodiment of theautomated, computer-controlled system of the present invention;

FIG. 4 is a sketch of certain signal waveforms which serves to definereceiver signal detect assert and deassert times; and

FIG. 5 is a sketch of one end of an eye pattern associated with thetransmitter of an electro-optic module, depicting the method associatedwith the invention for measuring transmitter data dependent jitter.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

The invention involves an automated, computer-controlled system, and acorresponding method, for testing electro-optic modules. Significantly,the inventive system and inventive method permit electro-optic modulesto be tested in relatively short time periods, e.g., three (3) minutes,and at relatively low cost.

A preferred embodiment of the inventive, automated, computer- controlledsystem 10 is depicted in FIG. 3 and is useful for measuring a variety ofparameters (more fully described below) associated with an electro-opticmodule 20 (which is not an integral part of the system 10) to be tested.It is assumed that the module 20 includes either a transmitter 30, or areceiver 40, or both, as depicted in FIG. 3.

It should be noted that like most such electro-optic modules, it is alsoassumed that the transmitter and receiver ICs of the module 20 employemitter-coupled logic, and therefore it is assumed that the input to thetransmitter ICs of the module 20 must be a differential input while theoutput from the receiver ICs of the module 20 is also a differentialoutput. That is, it is assumed that the input to the transmitter ICs isa combination of an input signal (denominated I in FIG. 3) and aninverted form of that same input signal (denominated I-bar in FIG. 3),while the output of the receiver ICs is a combination of an outputsignal (denominated O in FIG. 3) and an inverted form of that sameoutput signal (denominated O-bar in FIG. 3.). However, the components ofthe inventive system 10 employ single inputs rather than differentialinputs. Consequently, the system 10 includes a single input-differentialoutput emitter-coupled logic driver 50 (which is omitted if unnecessary)which serves to convert single inputs to the transmitter ICs of themodule 20 into differential inputs. In addition, the system 10 includesan emitter-coupled logic driver 55 which serves to buffer the receiverICs of the module 20 for communication to other system components. Oneuseful emitter-coupled logic driver 50,55 is emitter-coupled logicdriver model number 100114 sold by the Signetics company of Sunnyvale,Calif.

Significantly, as depicted in the lower left-hand corner of FIG. 3, thesystem 10 includes an electronic personal computer (PC) 70, such as a PCsold by the International Business Machines Corporation (IBM) under thetrademark PS/2, and preferably the mod 80 version of this particular PC.In the operation of the inventive system, a computer program associatedwith the invention, described below, is loaded into the PC 70, whichthen serves to control the various components of the system 10.

The PC 70 sends commands to, and receives information from, almost allof the components of the system 10 through a general purpose-interfacebus 80, such as bus model number MC-GPIB sold by the NationalInstruments company of Austin, Tex. However, certain control signals arecommunicated by the PC 70 to certain components of the system 10 througha so-called data in/data out bus 90, such as bus model numberMC-DIDO-32F sold by the National Instruments company, as more fullydescribed below.

In connection with the electro-optic module 20 to be tested, it shouldbe noted that the inventive system 10 includes a programmable powersupply 60, such as programmable power supply model number 6624A sold bythe Hewlett-Packard company of Santa Clara, Calif., which serves toprovide power to the module 20 during testing. This power supply 60communicates with the PC 70 via bus 80. It should also be noted that thePC 70 transmits enabling control signals (denominated DIDO 1 in FIG. 3)to the transmitter 30 of module 20 via bus 90. Moreover, if the module20 includes a pinned ceramic substrate on which are mounted thetransmitter ICs and the receiver ICs, as is conventional, then one ofthe substrate pins is usually dedicated to providing a voltage signalindicative of the fact that an input signal to the receiver 40 is belowthe receiver threshold level. In such an event, this voltage signal(denominated DIDO 4 in FIG. 3), called the receiver signal detectthreshold signal, is communicated to the PC 70 via the bus 90.

As depicted in the upper left hand corner of FIG. 3, the inventivesystem 10 includes a programmable power supply 100, such as programmablepower supply model number 6624A sold by the Hewlett-Packard company.This power supply 100, which communicates with PC 70 via bus 80, servesto supply power to a multivibrator 110. When powered by the power supply100, the multivibrator 110 communicates enabling and disabling clocksignals to a serial pattern generator, described below. These same clocksignals are also communicated to a programmable digital oscilloscope250, also described below.

As also shown in the upper left-hand corner of FIG. 3, and as mentionedabove, the inventive system 10 also includes a serial pattern generator120 having an internal clock 130. The serial pattern generator 120,which communicates with the PC 70 via the bus 80, serves to generateeither uniform, evenly spaced, square wave digital electrical signals orpseudo-random digital electrical signals, such as the so-called (2**7)-1pseudo-random pattern (see, e.g., the operation manual published by theAnritsu company of Tokyo, Japan, entitled "Error Rate MeasuringEquipment, ME522A", pages 3-21 and 3-22 for a description of the(2**7)-1 pseudo-random pattern), or other user defined patterns, attransmission speeds of interest, e.g., 200 megabits per second (Mb/s).One such useful serial pattern generator is serial pattern generatormodel number ME522A sold by the Anritsu company of Tokyo, Japan. Itshould be noted that the internal clock 130 of the serial patterngenerator 120 serves to generate evenly spaced, square wave clock pulsesat a transmission speed which is identical to that of either the uniformsquare wave pattern or the pseudo-random pattern.

The serial pattern generator 120 is electrically connected to amicrowave switch 140, such as microwave switch model number 34530A soldby the Hewlett-Packard company. This microwave switch is capable ofdirecting the digital electrical signals generated by the serial patterngenerator 120 to either of two output ports 142, 144. The choice ofoutput port is controlled by a switch control unit 150, such as switchcontrol unit model number 3488A sold by the Hewlett-Packard company. Theswitch control unit 150 is, in turn, controlled by the PC 70 via bus 80.

The output port 142 of the microwave switch 140 is electricallyconnected to a light-emitting, electro-optic transducer 160, such as asemiconductor laser or an LED, which communicates with the PC 70 via bus80. If, for example, a semiconductor laser is employed, then one suchuseful semiconductor laser is semiconductor laser model number 8155Asold by the Hewlett-Packard company. This particular semiconductor laseris capable of emitting digital optical signals at a wavelength of 1300nm and at a transmission speed of 200 Mb/s. Significantly, theextinction ratio (a term defined below) of this particular semiconductorlaser is about 9.0, whereas the minimum extinction ratios of most of thesemiconductor lasers employed in electro-optic modules is typicallyabout 4.0. The significance of this fact is explained below.

The digital optical signals produced by the electro-optic transducer 160in response to digital electrical signals generated by the serialpattern generator 120 are communicated via an optical fiber, e.g., asingle mode optical fiber having a core diameter of 9.0 micrometers, toan optical attenuator 170, which communicates with the PC 70 via bus 80.One such useful optical attenuator is optical attenuator model number8157A sold by the Hewlett-Packard company. The optical attenuator 170 inturn communicates attenuated digital optical signals, via anotheroptical fiber, to an optical splitter 180, such as optical splittermodel number ACS19C-1.3-9 sold by JDS Fitel,Inc. of Ottawa, Canada. Theoptical splitter 180 serves to split an incoming light signal into twosignals, i.e., 90% of the incoming light is communicated via an opticalfiber to the receiver 40 of the electro-optic module 20, while 10% ofthe incoming light is communicated via another optical fiber to anoptical input port 202 of an optical switch 200. One such useful opticalswitch is optical switch model number CC-S-9-5-L-R-DO-R sold by JDSFitel, Inc. The optical switch is also capable of receiving opticalsignals through an optical input port 204, as well as the optical inputport 202, with the choice of input port being determined by controlsignals received from switch control unit 150. The optical output ofoptical switch 200 is in turn communicated via an optical fiber 205 tooptical power meter 210. One such useful optical power meter is opticalpower meter model number 8152A sold by the Hewlett-Packard company.

As noted above, the optical splitter 180 serves to communicate 90% ofthe light received by the splitter to the receiver 40 of the module 20.The receiver 40, in turn, generates a corresponding differential output,which includes output O and corresponding, inverted output O-bar. Thisdifferential output is buffered by the emitter- coupled logic driver 55and the inverted output of driver 55 is terminated into a 50 ohm load.The data output of the driver 55 is then communicated to a serialpattern comparator 220, which serves to compare the digital electricalsignal produced by the receiver 40 to the corresponding digitalelectrical signal generated by the serial pattern generator 130. Onesuch useful serial pattern comparator is serial pattern comparator modelnumber ME522A RX sold by the Anritsu company. The serial patterncomparator 220 remains in sync with the serial pattern generator 120because it receives clock signals from the internal clock 130 of thesignal pattern generator 120 through a time delay unit 230. One suchuseful time delay unit includes a so-called mainframe unit, identifiedby model number 8080A, and so-called plug-in units, identified by modelnumbers 8092A and 8093A, sold by the Hewlett-Packard company. The timedelay effected by this time delay unit is determined by pushing buttonson the front of this unit. To avoid the need for human intervention,switches on the time delay unit are electrically closed by anelectro-mechanical relay unit 240, which receives control signals(denominated DIDO 2 and DIDO 3 in FIG. 3) from the PC 70 via the bus 90.

As shown in FIG. 3, the outputs 0 and O-bar, produced by the receiver40, are both also communicated to a programmable digital oscilloscope250 through 10x oscilloscope probes. This oscilloscope, whichcommunicates with the PC 70 via bus 80, receives clock signals from theinternal clock 130 of the serial pattern generator 120 via the timedelay unit 230, as well as clock signals from the multivibrator 110. Onesuch useful programmable digital oscilloscope is oscilloscope model CSA404 sold by the Tektronix company of Beaverton, Oreg.

As noted above, the microwave switch 140 is capable of switching thedigital electrical signals generated by the serial pattern generator 120to either output port 142 or output port 144. As shown in FIG. 3, theoutput port 144 is electrically connected, and thus serves tocommunicate the digital electrical signals generated by the serialpattern generator 120, to the emitter-coupled logic driver 50. Thelatter, in turn, serves to communicate received digital electricalsignals to the transmitter ICs of the module 20 in differential form.

When the transmitter 30 receives a digital electrical signal, itproduces a corresponding digital optical signal which is communicated,via an optical fiber 265, to an optical splitter 260 of the system 10,which is identical to the optical splitter 180. That is, the opticalsplitter 260 communicates 10% of an incident optical signal to inputport 204 of optical switch 200 and 90% of the incident optical signal toan optical input port 251 of the oscilloscope 250.

In the operation of the inventive system 10, when, for example, testsare to be performed on the receiver 40 of module 20, then, under thecontrol of the PC 70, the serial pattern generator 120 will generate adigital electrical signal which is communicated to the electro-optictransducer 160 via the microwave switch 140. The electro-optictransducer 160 will generate a corresponding digital optical signal,which is communicated to the optical splitter 180 via the opticalattenuator 170. The optical splitter 180 will divert 10% of the incidentdigital optical signal to the optical switch 200 and then to the opticalpower meter 210. Simultaneously, the optical splitter 180 will divert90% of the incident digital optical signal to the receiver 40 throughoptical fiber 45, which will then produce a corresponding digitalelectrical signal, which is communicated via the emitter-coupled logicdriver 55 to the serial pattern comparator 220.

If tests are to be performed on the transmitter 30 of the electro-opticmodule 20, then, under the control of the PC 70, the serial patterngenerator 120 will generate a digital electrical signal which iscommunicated to the emitter-coupled logic driver 50 via the microwaveswitch 140. The transmitter 30 will, in turn, produce a correspondingdigital optical signal, which is communicated to the optical splitter260. This splitter will divert 10% of the incident digital opticalsignal to the optical switch 200 and then to the optical power meter210. This splitter will also divert 90% of the incident digital opticalsignal to port 251 of the programmable digital oscilloscope 250.

As noted, the inventive system 10 is controlled by the PC 70. In thisregard, the invention also involves a computer program which is loadedinto the PC 70, which computer program serves to effectuate the testingmethod associated with the invention. This computer program includes anumber of subroutines, each of which is used in measuring a particularreceiver parameter or a particular transmitter parameter. Each of thesesubroutines, which are individually useful, are described below withreference to the attached listings, labeled Subroutine A, Subroutine B,etc. These listings do not, however, contain lines of correspondingsource code, which would have been very difficult for the reader tocomprehend. Rather, these listings contain lines of comments whichdescribe the corresponding source code, and thus these lines of commentsserve as a kind of pseudo-code.

Attached Subroutine A is used to effectuate the method associated withthe invention for measuring receiver sensitivity. Before describing thissubroutine, it should be noted that the measurement method underlyingthis subroutine does not assume that the slope of Q versus P (expressedin milliwatts) is that predicted by theory, as is the case with previoussuch methods. This assumption is avoided because a variety of factors,such as mistakes in the processes used to manufacture the electro-opticmodules, often lead to slopes which are different from the theoreticallypredicted slope. Therefore, the bit error rates (BERs) corresponding tothree different values of optical power are measured. The threecorresponding values of Q are then calculated using a version ofEquation (2) in which the integral in Equation (2) is approximated bythe first three terms of a power series representation of this integral,which assumes that Q is large. (In this regard, see equation 26.2.12 inthe mathematical handbook edited by Abramowitz and Stegun and entitled"Handbook of Mathematical Functions".) That is, the three values of Qare calculated using the formula ##EQU3## These three calculated valuesof Q, and the corresponding values of P, then represent three datapoints, to which is fitted a linear- least-squares-fit approximation.Thus, the slope of Q versus P is , in effect, determined empirically,rather than derived from theory. The value of Q corresponding to adesired BER is then calculated using Equation (3). Thelinear-least-squares-fit approximation is then extrapolated to thiscalculated value of Q, to determine the corresponding value of P.

Significantly, Subroutine A does not determine receiver sensitivity justat the center of the corresponding eye pattern. Rather, after the centerof the eye pattern has been located, and assuming the width of the eyepattern is sufficiently large, receiver sensitivity is also measured at,for example, -0.7 nanoseconds (ns) and +0.7 ns from the center of theeye pattern. These displacements from the center of the eye pattern arechosen to conform to the time interval over which the deserializerintegrated circuit device to be used in conjunction with the moduleunder test is capable of sampling the electrical pulses produced by thereceiver of the module.

With reference now to Subroutine A, step (1) is a command from the PC 70to the power supply 60 to provide electrical power to the device undertest (DUT) at an appropriate voltage, e.g., 5.0 volts.

Step (2) denotes a command from the PC 70 to switch control unit 150 toset microwave switch 140 so that the output of serial pattern generator120 will be communicated to output port 142 and to set optical switch200 so that the input to the optical switch 200 is via input port 202.

Step (3) is a command from PC 70 to serial pattern generator 120 togenerate evenly spaced square waves at a transmission speed of interest,e.g., 200 Mb/s. As a consequence, the light-emitting electro-optictransducer 160 will generate corresponding, evenly spaced optical squarewaves which will be received by the receiver 40 of the module 20 undertest.

Step (4) is a command from PC 70 to the programmable digitaloscilloscope 250 to switch to the input channel carrying input from thereceiver 40 of the module 20.

Step (5) is a command from PC 70 to the oscilloscope 250 specifyingreceiver channel range (in volts/division, e.g., 0.2 volts/division) andoffset (the voltage corresponding to the center graticule of theoscilloscope, e.g., 0.335 volts).

Step (6) is a command from the PC 70 to the oscilloscope 250 to triggeron the leading edge of an input waveform, i.e., to display the waveformin response to the leading edge of the waveform.

Step (7) is a command from the PC 70 to the oscilloscope 250 in whichthe oscilloscope time base, i.e., nanoseconds/division (e.g., 1.0nanoseconds/division), and delay, i.e., the amount of time theoscilloscope should delay before initiating a waveform trace (e.g., 0.0nanosecond delay), are defined.

Step (8) is a command from the PC 70 to the oscilloscope 250 to employthe average mode, which means that the oscilloscope is to displaywaveforms consisting of points, each of which is the average of acurrent point and of a corresponding previous point, so as to producerelatively smooth waveforms.

Step (9) is a command from the PC 70 to the oscilloscope 250 todetermine the upper and lower voltages corresponding to the receiverwaveform, in order to ensure that the electrical output of receiver 40is switching in response to the square wave optical pulses produced bythe light-emitting electro-optic transducer 160.

Step (10) is a command from the PC 70 to the oscilloscope 250 to receiveclock pulses from the internal clock 130 of the serial pattern generator120.

Step (11) is a command from the PC 70 to the serial pattern generator120 to generate the (2**7)-1 pseudo-random pattern.

Step (12) is a command from the PC 70 to the serial pattern comparator220 to compare incoming signals to the (2**7)-1 pseudo-random pattern.

Step (13) is a command from the PC 70 to the oscilloscope 250 to employthe normal mode, i.e., the persist mode, in which new waveforms aresuperimposed on old waveforms so as to produce an eye pattern.

Step (14) is a command from the PC 70 to the oscilloscope 250 to triggerin response to clock pulses from the internal clock 130 of the serialpattern generator 120.

Step (15) is a command from the PC 70 to the serial pattern comparator220 in which the threshold voltage for the comparator is defined as 0.0volts.

Step (16) is a command from the PC 70 to the optical power meter 210 tocommunicate received optical power in units of dB (instead of, forexample, watts).

Step (17) is a command from the PC 70 to the optical power meter 210defining a reference power level related to the difference between theoptical powers communicated to the receiver 40 and the optical powermeter 210, so that the optical power meter automatically communicatesthe power received by the receiver 40 to the PC 70. This reference powerlevel is determined in accordance with the calibration procedure,described below.

Step (18) is a command from the PC 70 to the optical power meter 210instructing the optical power meter to trigger, i.e., to take an opticalpower reading and communicate this reading to the PC 70, upon receivinga command from the PC 70.

Step (19) involves a series of commands from the PC 70 to several systemcomponents to determine the width of the eye pattern corresponding tothe receiver 40 of the module 20, and to determine the receiverthreshold power at the center of the eye pattern. That is, step (19a) isa command to the serial pattern comparator 220 to sample all incomingbits from the receiver 40 over a time period of, for example, 1.0seconds. Step (19b) involves control signals to the electro-mechanicalrelay unit 240 to adjust the time delay unit 230 to produce a timedelay, e.g., -3.8 nanoseconds, corresponding to the estimated (on thebasis of previous experience) center of the eye pattern. Step (19c) is acommand to the optical attenuator 170 to attenuate the optical powerbeing coupled into the receiver 40 so that receiver threshold power ismeasured at an input optical power, e.g., -32 dB, at which the entireeye pattern is displayed on the oscilloscope screen. Step (19d) is acommand from the PC 70 to the optical attenuator 170 to decrement powerto the receiver 40 in steps of, for example, 0.2 dB, until the serialpattern comparator 220 detects errors in the center of the eye pattern.At that point, the optical attenuator is to increase optical power tothe receiver by 0.3 dB, so that all errors in the center of the eyepattern are eliminated, with the resulting power constituting receiverthreshold power at the center of the eye pattern. This is significant inthat the center of the eye is a function of the received-optical power.Therefore the center of the eye is measured at the receiver thresholdpower which is sufficiently close to the BER measurement pointsdescribed below. Step (19e) involves a series of commands for obtainingthe width of the eye pattern. That is, step (19e-1) is a command fromthe PC 70 to the serial pattern comparator 220 to sample all incomingbits from the receiver 40 over a time period of, for example, 1.0seconds. Step (19e-2) is a command from the PC 70 to theelectro-mechanical relay unit 240 to adjust the time delay unit 230 toproduce a time delay approximately corresponding to the right-hand edgeof the eye pattern. The width of an eye pattern is typically 1.4 ns, andtherefore this right-hand edge is about 0.7 ns from the center of theeye pattern. Step (19e-3) is a command from the PC 70 to theelectro-mechanical relay unit 240 to adjust the time delay unit 230 toincrement or decrement the time delay in steps of, for example, 0.1 ns,until the right-hand edge of the eye pattern is found, i.e., until theserial pattern comparator first detects errors. Steps (19e-4) and(19e-5) serve to determine the left-hand edge of the eye pattern. Instep (19e-6), the delay times corresponding to the right-hand andleft-hand edges of the eye pattern are saved. Step (19f) isself-explanatory.

Step (20) is a command from the PC 70 to the electro-mechanical relayunit 240 to adjust the time delay unit 230 to achieve a time delay of-0.7 ns from the center of the eye pattern.

Step (21) involves a series of commands for obtaining a power level atwhich the serial pattern comparator 220 measures a BER between 10**7 and10**-8. That is, step (21a) is a command from the PC 70 to the serialpattern comparator 220 to sample all bits from the receiver 40 over atime period of, for example, 1.0 seconds. Step (21b) is a command fromthe PC 70 to the optical attenuator 170 to increment or decrementoptical power to the receiver 40 until the serial pattern comparator 220measures a BER less than, for example, 10**-2. In step (21c), the BER ischecked to see if it is between 10**-7 and 10**-8. If not, and if, forexample, the first BER is greater than 5×10**-4, then in step (21d) theoptical power to the receiver 40 is increased by, for example, 0.4 dB.In step (21e), the BER is checked again to see if it is between 10**-7and 10**-8. If not, then in step (21f) the values of Q corresponding tothe first two measured values of BER are calculated using Equation (3).These calculations involve guessing values of Q, and subtracting theright-hand side from the left-hand side of Equation (3) until thisdifference is zero, or essentially zero. A straight line is then fittedto the two calculated values of Q in relation to the correspondingvalues of P. Equation (3) is thereafter used to calculate the value of Qcorresponding to a BER of, for example, 10**-8. The above- mentionedstraight line relation between Q and P is extrapolated to determine thevalue of P corresponding to the last calculated value of Q. This lastvalue of P then constitutes the receiver sensitivity at a BER of 10**-8.Step (21g) involves fine adjustments to the above procedure, if needed.

In step (22), the power level corresponding to a BER of 10**-8, asdetermined in step (21), is twice decremented by 0.4 dB, to obtain atotal of three power levels, to be used in succeeding steps.

In step (23), the three power levels determined in step (22) are saved.

Step (24) is a command from the PC 70 to the serial pattern comparator220 to sample all bits from the receiver 40 over a time period of 2.0seconds.

In step (25), the BERs corresponding to the three power levels of step(22) are measured.

In step (26), the values of Q corresponding to the three measured valuesof BER are calculated using Equation (3). These three values of Q andthe three corresponding values of P define three data points, to whichis fitted a linear-least-squares-fit approximation. Equation (3) is nowused to calculate the value of Q corresponding to the desired value ofBER, e.g., 10**-15. The linear-least-squares-fit approximation is nowextrapolated to this value of Q, to determine the corresponding value ofP.

A significant aspect of the invention, which is incorporated into step(27), is the recognition that receiver sensitivity is a function of theextinction ratio associated with the electro-optic transducer 160 usedto measure receiver sensitivity. Yet another significant aspect of theinvention is the finding that by adding a correction factor (CR) to areceiver sensitivity measurement made using a first extinction ratio,that the value of receiver sensitivity corresponding to a secondextinction ratio is readily determined. Moreover, it has been determinedthat the above CR is given by

    CR=10*log((LSER2+1)/(LSER2-1))-10*log((LSER1+1)/(LSER1-1)),(4)

where LSER1 is the extinction ratio used in measuring receiversensitivity, while LSER2 is the extinction ratio for which receiversensitivity is desired. In this regard, if, for example, theelectro-optic transducer 160 is a semiconductor laser exhibiting anextinction ratio of 9.0, rather than 4.0, as is conventional, then instep (27) a CR is added to the receiver sensitivity measured in step(26), where the CR is given by

    CR=10*log((4+1)/(4-1))-10*log((9+1)/(9-1)).

It must be noted that CR is in units of dB, and is added to the value ofmeasured receiver sensitivity, also expressed in dB. It should also benoted that the value of extinction ratio used in measuring receiversensitivity is itself measured using the corresponding calibrationprocedure, described below.

In step (28), the Correlation between the three data points of step (26)and the linear-least-squares-fit approximation is calculated. If, forexample, all three data points fall on the linear-least-squares-fitapproximation, then the correlation will be 1.0. Preferably, thecorrelation should be at least 0.98. In addition, the slope of thelinear-least-squares-fit approximation is determined.

In step (29), the receiver sensitivity determined above is comparedagainst a corresponding specification.

Steps (30)-(38) are identical to steps (20)-(29), only the delay timecorresponds to +0.7 ns.

Attached subroutine B is used to effectuate the method associated withthe invention for measuring receiver pulse width distortion (RPWD). Thisreceiver parameter is defined as

    RPWD=((Tp-Tn)/(Tp+Tn))×100,                          (5)

where Tp denotes the width of a positive pulse produced by the receiver40 and Tn denotes the width of a negative pulse produced by the receiver40, and where the width of each pulse is measured at a voltage levelexactly half-way between the top and bottom of the pulse while thereceiver is being optically driven by uniform, evenly spaced, squarewave optical pulses at a transmission speed of interest.

With reference to subroutine B, steps (1) and (2) are self- explanatory.

Step (3) is a command from the PC 70 to the serial pattern generator 120to generate uniform, evenly spaced square waves at a transmission speedof interest, e.g., 200 Mb/s. As a consequence, the light-emittingelectro-optic transducer 160 will generate corresponding, uniform,evenly spaced square waves which will be received by the receiver 40 ofthe module 20 under test.

Step (4) is self-explanatory.

Step (5) is a command from PC 70 to the oscilloscope 250 specifyingreceiver channel range, e.g., 0.2 volts/division, and offset, e.g.,0.335 volts is specified as the voltage corresponding to the centergraticule of the oscilloscope.

Step (6) is self-explanatory.

Step (7) is a command from the PC 70 to the oscilloscope 250 specifyingtime base, e.g., 2.0 ns/division, and delay, e.g., 0.0 ns.

Steps (8), (9) and (10) are self-explanatory.

Step (11) is a command from the PC 70 to the optical attenuator 170 toattenuate the optical power being coupled into the receiver 40 so as toperform the test at a desired optical power, e.g., -23 dB.

Steps (12) and (13) are self-explanatory.

Step (14) is a command from the PC 70 to the oscilloscope 250 orderingthe oscilloscope to check that the voltage difference between the topand bottom of the waveform is sufficient, e.g., at least 0.08 volts.

In step (15), Tp and Tn are measured. That is, steps (15a)-(15e) involvean examination of adjacent receiver pulses to distinguish between apositive pulse (i.e., a pulse having an upwardly inclined leading edge)and a negative pulse (i.e., a pulse having a downwardly inclined leadingedge). Based upon these distinctions, the width of a positive pulse ismeasured to obtain Tp and the width of a negative pulse is measured toobtain Tn.

In step (16), RPWD is calculated, using Equation (5).

Attached subroutine C is used to effectuate the method associated withthe invention for measuring receiver signal detect threshold (RSDT).That is, steps (1)-(6) are self-explanatory. Step (7) is a command fromthe PC 70 to the optical attenuator 170 to decrement optical power tothe receiver 40 in increments of, e.g., 0.2 dB, until the RSDT voltagesignal (DIDO 4) is detected. The corresponding value of optical powercoupled into the receiver 40 constitutes RSDT. In step (9), CR is addedto RSDT and in step (10), a pass/fail determination is made.

Attached subroutine D is used to effectuate the method associated withthe invention for measuring receiver signal detect assert time (Ta) andreceiver signal detect deassert time (Td). That is, in accordance withthis method, the signal pattern generator 120 is used to generate the(2**7)-1 pseudo-random pattern at a transmission speed of interest,e.g., 200 Mb/s. This pseudo-random pattern is communicated to theelectro-optic transducer 160, which generates a correspondingpseudo-random optical pattern communicated to the receiver 40. While thepseudo-random generator 120 is operating, the power supply 100 is usedto supply power to the multivibrator 110, which sends enabling anddisabling clock signals to the serial pattern generator 120 at afrequency of, for example, 200 Hertz. These clock signals are depictedin FIG. 4, as is the pseudo-random pattern, with the former beingdenoted by the letter A and the latter being denoted by the letter B inFIG. 4. As shown, when the multivibrator 110 generates a positive pulse(which is necessarily much longer than any of the individual pulsesgenerated by the signal pattern generator 120), the signal patterngenerator 120 is enabled. Similarly, when the multivibrator 110generates a negative pulse, the signal pattern generator is disabled.

In addition to depicting the enabling and disabling clock signalsgenerated by the multivibrator 110 and the pseudo-random patterngenerated by the signal pattern generator 120, FIG. 4 also depicts thevoltage signal produced by the module pin dedicated to generating theRSDT voltage, which signal is denoted by the letter C. As shown in FIG.4, when the signal pattern generator 120 is disabled by a disablingclock pulse from the multivibrator 110, there is a time lag in thecorresponding response in the RSDT voltage signal, which is defined asTd. Similarly, as shown in FIG. 4, when the signal pattern generator 120is enabled by an enabling clock pulse from the multivibrator 110, thereis also a time lag in the corresponding response in the RSDT voltagesignal, which is defined as Ta.

With reference to subroutine D, step (1) is self-explanatory.

Step (2) is self-explanatory, except that "Gate sync" means that theclock pulses generated by the multivibrator are to trigger theoscilloscope 250.

Step (3) is a command from the PC 70 turning on the power supply 100,and thereby providing power to the multivibrator 110.

In step (4), "Gate" refers to the multivibrator 110, and thecorresponding "Gate" input channel 252 range is, for example, 0.05volts/division, and the corresponding offset is, for example, 0.0 volts.

In step (5), the channel range and offset are specified for step (13),the difference between the upper and lower "Gate" input channel 252, ofthe oscilloscope 250 on which the RSDT voltage signal is to becommunicated. This channel range is, for example, 0.2 volts/division,and the corresponding offset is, for example, 3.45 volts.

In step (6), the oscilloscope 250 is commanded to trigger in response tothe "Gate" waveform.

In step (7), the time base and delay for the oscilloscope 250 arespecified. These are, for example, 100 microseconds/division and -500microseconds, respectively, which permits both the "Gate" waveform andthe RSDT waveform to be displayed simultaneously. Steps (8)-(10) areself-explanatory. In step (11), the optical power to be coupled into thereceiver 40 during the test, e.g., -27 dB, is specified.

Step (12) is self-explanatory.

In step (13), the difference between the upper and lower "Gate" waveformvoltages is determined by the oscilloscope 250 to make certain thisdifference is greater than, for example, 0.04 volts. In step (14), thedifference between the upper and lower RSDT waveform voltages isdetermined by the oscilloscope 250 to make certain this difference isgreater than, for example, 0.15 volts.

In step (15), the positive (upwardly inclined) leading edges of the"Gate" and RSDT waveforms are identified.

In step (16), the results obtained in step (16) are converted tomicroseconds and saved.

In step (17), Ta is calculated and checked to see if it conforms to acorresponding specification.

In step (18), the negative (downwardly inclined) leading edges of the"Gate" and RSDT waveforms are identified.

In step (19), the results obtained in step (18) are converted tomicroseconds and saved.

In step (20), Td is calculated and checked to see if it conforms to acorresponding specification.

Attached subroutine E is used to effectuate the method associated withthe invention for measuring transmitter average power. In this regard,it should be understood that when the transmitter 30 of the module 20 isproducing a digital optical signal, that the transmitter is switchingbetween a relatively high optical output power and a relatively lowoptical output power, and that transmitter average power denotes theaverage of these two optical powers.

With reference to subroutine E, step (1) is self-explanatory.

Step (2) denotes a command from the PC 70 to switch control unit 150 toset microwave switch 140 so that the output of serial pattern generator120 will be communicated to output port 144 and to set optical switch200 so that the input to the optical switch is via input port 204.

Step (3) is a command from PC 70 to serial pattern generator 120 togenerate the (2**7)-1 pseudo-random pattern. As a consequence, thetransmitter 30 of the module 20 will produce a corresponding,pseudo-random optical pattern, which will be communicated via theoptical switch 200 to the optical power meter 210.

Step (4) is self-explanatory.

Step (5) is a command-from the PC 70 to the optical power meter 210defining a reference average power level related to the differencebetween the average optical power generated by the transmitter 30 andthe average optical power communicated to the optical power meter 210,so that the optical power meter communicates the average optical powergenerated by the transmitter 30 to the PC 70.

Step (6) is a command from the PC 70 to the optical power meter 210 totrigger continuously, i.e., to constantly monitor average optical power.

Step (7) is a command from the PC 70 to the optical power meter 210requesting the most recent value of average optical power generated bythe transmitter 30.

Step (8) is a check on whether the transmitter is effectively dead. Thatis, if the most recent value of average optical power is, for example,less than -50 dB, then it is assumed that the transmitter is effectivelydead.

Step (9) involves a comparison between the most recently measured valueof average optical power and corresponding specification.

Attached subroutine F is used to effectuate the method associated withthe invention for measuring transmitter rise and fall times. In thisregard, it should be understood that transmitter rise time denotes theamount of time required by the upwardly inclined portion of atransmitter optical pulse to rise from 20% to 80% of the pulse topline,relative to the pulse baseline, when the transmitter is driven byuniform, evenly spaced, square wave electrical pulses at a transmissionspeed of interest. Similarly, it should be understood that transmitterfall time denotes the amount of time required by the downwardly inclinedportion of a transmitter optical pulse to fall from 80% to 20% of thepulse topline, relative to the pulse baseline, when the transmitter isdriven as described above.

With reference to subroutine F, steps (1)-(3) are self-explanatory.

In step (4), it should be noted that the transmitter channel range andoffset are automatically chosen by the oscilloscope 250 so that thetransmitter waveform fits on the screen. Still, it should also be notedthat the transmitter channel range is typically chosen to be 0.0001volts/division and the offset is 0.0 volts. Moreover, as noted in step(4), the coupling is AC, and therefore the waveform swings around 0.0volts.

Step (5) is self-explanatory.

In step (6), the time base is, e.g., 2.0 ns/division, and the delay is,e.g., 0.0 ns.

Steps (7) and (8) are self-explanatory.

In step (9), a sufficient amplitude is, for example, 0.00001 volts.

Steps (10)-(14) are self-explanatory.

Attached subroutine G is used to effectuate the method associated withthe invention for measuring transmitter extinction ratio. In thisregard, as noted above, when the transmitter 30 produces optical pulses,it switches between a relatively high optical power level and arelatively low optical power level. In addition, it should be understoodthat transmitter extinction ratio denotes the ratio of these powerlevels when the transmitter is electrically driven by uniform, evenlyspaced, square wave pulses transmitted at a transmission speed ofinterest.

With reference to subroutine G, steps (1) and (2) are self- explanatory.

In step (3), the transmission speed of the square wave pattern is, forexample, 40 Mb/s.

In step (4), the transmitter channel range and offset are automaticallychosen by the oscilloscope 250 so that the transmitter waveform fits onthe screen. In addition, the coupling is DC.

Step (5) is self-explanatory.

In step (6), the time base is, for example, 10 ns/division and the delayis, for example, 0.0 ns.

Steps (7) and (8) are self-explanatory.

In step (9), a sufficient amplitude is, for example, 0.00001 volts.

Steps (10)-(12) are self-explanatory.

Attached subroutine H is used to effectuate the method associated withthe invention for measuring transmitter duty cycle distortion (TDCD).This transmitter parameter is defined as

    TDCD=(Tp'-Tn')/2,                                          (6)

where Tp' denotes the width of a positive pulse produced by thetransmitter 30, Tn' denotes the width of a negative pulse produced bythe transmitter 30, and where the width of each pulse is measured at avoltage level exactly half-way between the top and bottom of the pulsewhile the transmitter is being electrically driven by uniform, evenlyspaced, square wave pulses at a transmission speed of interest.

With reference to subroutine H, steps (1) and (2) are self- explanatory.

In step (3), the transmission speed is, for example, 200 Mb/s.

In step (4), the transmitter channel range and offset are automaticallychosen by the oscilloscope so that the transmitter waveform fits on thescreen. The coupling is AC.

Step (5) is self-explanatory.

In step (6), the time base is, for example, 2 ns/division and the delayis, for example, 0.0 ns.

Steps (7) and (8) are self-explanatory.

In step (9), a sufficient amplitude is, for example, 0.00001 volts.

In step (10), the reference voltage for the oscilloscope is set to 0.0volts.

Steps (11) and (12) are self-explanatory.

Attached subroutine I is used to effectuate the method associated withthe invention for measuring the root mean square transmitter datadependent jitter (TDDJ). In this regard, and as depicted in FIG. 5, itshould be understood that this transmitter parameter involves theformation of an eye pattern associated with the transmitter, when thetransmitter is electrically driven by a digital pattern called the K28.5pattern. (Regarding the K28.5 pattern see, e.g., A. X. Widmer et al, "ADC-Balance, Partitioned-Block, 8B/10B Transmission Code", IBM Journal ofResearch and Development, Vol. 27, No. 5, September 1983.) In addition,as also depicted in FIG. 5, this parameter further involves theformation of a box around the center of the X-like voltage crossings atone end of the transmitter eye pattern, and the formation of a histogramrelated to the number of voltage crossings across the center of the X.TDDJ is just the standard deviation associated with this histogram.

With reference to subroutine I, steps (1) and (2) are self- explanatory.

In step (3), the transmission speed of the square wave pattern is, forexample, 200 Mb/s.

In step (4), the time base is, for example, 2 ns/division and the delayis, for example, 0.0 ns.

In step (5), it should be noted that the channel range and offset areautomatically chosen by the oscilloscope 250 so that the transmitterwaveform fits on the screen. Also, the coupling is AC.

Steps (6)-(8) are self-explanatory.

In step (9), a sufficient amplitude is, for example, 0.00001 volts.

Step (10) is a command from the PC 70 to the serial pattern generator togenerate the K28.5 pattern.

Step (11) is a command from the PC 70 to the oscilloscope 250 to switchto normal acquisition, i.e., the persist mode, so as to generate an eyepattern.

Step (12) is a command from the PC 70 to the oscilloscope 250 to triggeroff the clock pulses generated by the internal clock 130 of the serialpattern generator 120, and specifically to trigger off the negativeclock pulse transitions.

Step (13) involves the formation of a box on the oscilloscope screenaround the center of the X-like voltage crossings at one end of the eyepattern on the screen. That is, in step (13a), colors are assigned toeach pixel indicative of the number of times a pixel has beenilluminated. In step (13b), the vertical voltage scale is set toabsolute values of voltage, rather than relative voltage values. In step(13c), the left and right sides of the box are defined, with thehorizontal time scale on the screen extending from 0% to 100%, therebyencompassing the entire screen display. In step (13d), the top andbottom of the transmitter waveform is measured, and the distal parameteris set at 68% of the height of the waveform, the proximal parameter isset at 15% of the height of the waveform, and the mesial parameter isset at 50% of the height of the waveform. In step (13e), theoscilloscope loops, i.e., counts the number of points in the box, until,for example, at least 50 points are found. In step (13f), theoscilloscope performs the TDDJ measurement, using its internal program,i.e., the oscilloscope measures the standard deviation associated withabove-mentioned histogram. In step (13f), the result of the TDDJmeasurement in step (13e) is converted to picoseconds.

Step (14) is self-explanatory.

A significant advantage associated with the inventive system 10 is thefact that the optical fibers associated with the system are neverphysically moved during testing of modules. As a consequence, theinventive system 10 only needs to be calibrated about once a day. Thisfact should be contrasted with previous manual systems, where theoptical fibers are repeatedly moved, necessitating system calibrationsbetween each test. This difference is one of the reasons whyelectro-optic modules are tested so much more quickly using theinventive system 10.

To complete the present disclosure, the calibration procedures used inconnection with the inventive system 10 are described below, withreference to corresponding calibration subroutines.

With reference to Subroutine J, which relates to the optical power metercalibration procedure, step (1) is a command from the PC 70 to theoptical power meter 210 to set the optical power meter calibration valueand optical power meter reference value to 0.0 dB in preparation for thecalibration procedure.

Step (2) denotes a command from the PC 70 to the optical power meter 210to set the calibration factor to the value of the optical head lensloss, e.g., -0.09 dB.

Step (3) is a command from the PC 70 to the optical power meter 210 toset the wavelength at which the calibration measurement is to be made,e.g., 1309 nanometers.

Step (4) displays a message on the PC 70 display requesting that theoperator type in the optical power, e.g., -5.0 dB, at the output of a 3meter optical fiber, known hereafter as the floor optical fiber,connected to a stable laser source, known hereafter as the floor lasersource. The optical power measurement is made using a precision powermeter, to be known hereafter as the floor power meter.

Step (5) displays a message on the PC 70 display requesting the operatorto connect the optical fiber of the floor laser to the optical powermeter 210. The PC 70 then commands the optical power meter 210 tocommunicate the current optical power meter reading to the PC 70.

Step (6) calculates the difference in optical power between the floorlaser source-optical power and the optical power meter 210 readingobtained in step (5) and adds to this difference, the optical head lensloss.

Step (7) is a command from the PC 70 to the optical power meter 210 tostore the value calculated in step 6 as a calibration value.

Step (8) is a command from the PC 70 to the optical power meter 210 tocommunicate the current optical power to the PC 70.

Step (9) calculates the difference between the floor laser power and thepower received from the optical power meter 210. The difference is thencompared to a corresponding specification to determine if the valueshould be saved.

With reference to Subroutine K, which relates to the transmitter fixturecalibration procedure, step (1) is a command from the PC 70 to theoptical power meter 210 to set the optical power meter calibration valueand optical power meter reference value to 0.0 dB in preparation for thecalibration procedure.

Step (2) denotes a command from the PC 70 to the optical power meter 210instructing the optical power meter to continuously update its displayand to return the current display value when requested by the PC 70.

Step (3) is a command from the PC 70 to the optical power meter 210 toset the reference power level to 0.0 dB.

Step (4) is a command from the PC 70 to the optical power meter 210 toset the wavelength at which the calibration measurement is to be made,e.g., 1309 nanometers.

Step (5) displays a message on the PC 70 display requesting that theoperator connect the floor optical fiber to the FC end of a calibrationfiber, e.g., a duplex fiber with FC connectors on one end and a duplexreceptacle on the other end, the duplex receptacle of the calibrationfiber to the duplex connector of the system, and to connect thetransmitter fiber 265 to the optical power meter 210. The PC 70 thencommands the optical power meter 210 to communicate the current opticalpower meter reading to the PC 70.

Step (6) calculates the difference in optical power between the floorlaser source optical power and the optical power meter 210 reading. Thisis known as the transmitter fiber/fixture loss.

Step (7) compares the result of the calculation with the correspondingspecification to determine if the value should be saved and displays theresult.

With reference to Subroutine L, which relates to the transmitter linkcalibration procedure, step (1) is a command from the PC 70 to theswitch control unit 150 to set the optical switch 200 so that the inputto optical switch 200 is via input port 204.

Step (2) is a command from the PC 70 to the optical power meter 210 toset the optical power meter calibration value and optical power meterreference value to 0.0 dB in preparation for the calibration procedure.

Step (3) denotes a command from the PC 70 to the optical power meter 210instructing the optical power meter to continuously update its displayand to return the current display value when requested by the PC 70.

Step (4) is a command from the PC 70 to the optical power meter 210 toset the reference power level to 0.0 dB.

Step (5) is a command from the PC 70 to the optical power meter 210 toset the wavelength at which the calibration measurement is to be made,e.g., 1309 nanometers.

Step (6) displays a message on the PC 70 display requesting that theoperator connect the transmitter fiber 265 back to the optical splitter260, and the optical power meter fiber 205 back to the optical powermeter 210. The PC 70 then commands the optical power meter 210 tocommunicate the current optical power meter reading to the PC 70.

Step (7) calculates the difference in optical power between the floorlaser source minus the fiber/fixture loss, and the optical powerobtained in step 6. This is known as the transmitter link loss.

Step (8) is a command from the PC 70 to the optical power meter 210 toset the reference to the value obtained in step 7.

Step (9) is a command from the PC 70 to the optical power meter 210 tocommunicate the current optical power reading to the PC 70.

Step (10) compares the result of the calculation with the correspondingspecification to determine if the value should be saved and displays theresult.

With reference to Subroutine M, which relates to the receiver linkcalibration procedure, step (1) denotes a command from the PC 70 toswitch control unit 150 to set microwave switch 140 so that the outputof serial pattern generator 120 will be communicated to output port 142and to set optical switch 200 so that the input to the optical switch200 is via input port 202.

Step (2) is a command from the PC 70 to the optical power meter 210 toset the optical power meter calibration value and optical power meterreference value to 0.0 dB in preparation for the calibration procedure.

Step (3) denotes a command from the PC 70 to the optical power meter 210instructing the optical power meter to continuously update its displayand to return the current display value when requested by the PC 70.

Step (4) is a command from the PC 70 to the optical power meter 210 toset the reference power level to 0.0 dB.

Step (5) is a command from the PC 70 to the optical power meter 210 toset the wavelength at which the calibration measurement is to be made,e.g., 1300 nanometers.

Step (6) is a command from the PC 70 to the optical attenuator 170 toset the attenuation to 0.0 dB.

Step (7) displays a message on the PC 70 display requesting that theoperator connect the receiver side of the duplex connector 45 to theoptical power meter 210. The PC 70 then commands the optical power meter210 to communicate the current optical power meter reading to the PC 70.

Step (8) displays a message on the PC 70 display requesting that theoperator connect the optical power meter fiber 205 to the optical powermeter 210. The PC 70 then commands the optical power meter 210 tocommunicate the current optical power meter reading to the PC 70.

Step (9) calculates the difference in optical power between the readingsobtained in steps 7 and 8. This is known as the receiver link loss.

Step (10) is a command from the PC 70 to the optical power meter 210 toset the reference to the value obtained in step 9.

Step (11) is a command from the PC 70 to the optical power meter 210 tocommunicate the current optical power reading to the PC 70.

Step (12) compares the result of the calculation with the correspondingspecification to determine if the value should be saved and displays theresult.

With reference to Subroutine N, which relates to the frequency generatorcalibration procedure, step (1) determines the limits to which theresults will be compared, e.g., desired frequency of 100 MHz +/-1%,desired voltage amplitude of 1.0 volts +/-10%, desired voltage offset of0.0 volts +/-10%.

Step (2) denotes a command from the PC 70 to the switch control unit 150to set microwave switch 140 so that the output of serial patterngenerator 120 will be communicated to output port 144 and to set opticalswitch 200 so that the input to the optical switch 200 is via input port204.

Step (3) is a command from the PC 70 to the oscilloscope 250 to employthe normal mode, i.e., the persist mode, in which new waveforms aresuperimposed on old waveforms so as to produce an eye pattern.

Step (4) is a command from PC 70 to the oscilloscope 250 specifyingreceiver channel range (in volts/division, e.g., 0.2 volts/division) andoffset (the voltage corresponding to the center graticule of theoscilloscope, e.g., 0.0 volts).

Step (5) is a command from the PC 70 to the oscilloscope 250 to triggeron the leading edge of an input waveform, i.e., to display the waveformin response to the leading edge of the waveform.

Step (6) is a command from the PC 70 to the oscilloscope 250 in whichthe oscilloscope time base, i.e., nanoseconds/division (e.g., 3.0nanoseconds/division), and delay, i.e., the amount of time theoscilloscope should delay before initiating a waveform trace (e.g., 0.0nanosecond delay), are defined.

Step (7) is a command from the PC 70 to the oscilloscope 250 to employthe average mode, which means that the oscilloscope is to displaywaveforms consisting of points, each of which is the average of acurrent point and of a corresponding previous point, so as to smooth thewaveforms.

Step (8) displays a message on the PC 70 display requesting that theoperator connect the output of the frequency generator 150 to a channelof the oscilloscope.

Step (9) consists of several commands from the PC 70 to the oscilloscope250 requesting the frequency of the waveform (step 9a), the voltageamplitude of the waveform (step 9b), and the voltage offset of thewaveform (9c). At this point the operator must adjust the frequencygenerator until all parameters are within the specifications calculatedin step 1. When the parameters are satisfactorily adjusted, the keyboardtermination key is pressed by the operator (step 9d), e.g., enter key,and the values are saved.

With reference to Subroutine O, which relates to the oscilloscopecalibration procedure, step (1) displays a message on the PC 70 displayrequesting that the operator remove the optical fiber from the channel251 input and cover the input with a protective cap. A command is thensent from the PC 70 to the oscilloscope 250 to calibrate the channel251.

Step (2) displays a message on the PC 70 display requesting that theoperator remove the cable from channel 256 of the oscilloscope andconnect a spare cable from channel 256 to the oscilloscope calibratoroutput. A command is then sent from the PC 70 to the oscilloscope 250 tocalibrate the 256 channel.

Step (3) calibrates channel 255 using the method in step 2.

Step (4) calibrates channel 253 using the method in step 2.

Step (5) calibrates channel 254 using the method in step 2.

Step (6) displays the results of the calibration.

With reference to Subroutine P, which relates to the laser sourceextinction ratio calibration procedure, step (1) denotes a command fromthe PC 70 to the switch control unit 150 to set optical switch 200 sothat the input to the optical switch 200 is via input port 204.

Step (2) is a command from the PC 70 to the switch control unit 150 toset microwave switch 140 so that the output of the serial patterngenerator 120 will be communicated to output port 142.

Step (3) is a command from PC 70 to the serial pattern generator 120 togenerate evenly spaced square waves at a transmission speed of interest,e.g., 200 Mb/s. As a consequence, the light-emitting electro-optictransducer 160 will generate corresponding, evenly spaced optical squarewaves.

Step (4) is a command from the PC 70 to the oscilloscope 250 to employthe normal mode, i.e., the persist mode, in which new waveforms aresuperimposed on old waveforms so as to produce an eye pattern.

Step (5) is a command from PC 70 to the oscilloscope 250 specifyingreceiver channel range (in volts/division, e.g., 0.00005 volts/division)and offset (the voltage corresponding to the center graticule of theoscilloscope, e.g., 0.00015 volts).

Step (6) is a command from the PC 70 to the oscilloscope 250 to triggeron the leading edge of an input waveform, i.e., to display the waveformin response to the leading edge of the waveform.

Step (7) is a command from the PC 70 to the oscilloscope 250 in whichthe oscilloscope time base, i.e., nanoseconds/division (e.g., 5.0nanoseconds/division), and delay, i.e., the amount of time theoscilloscope should delay before initiating a waveform trace (e.g., -5.0nanosecond delay), are defined.

Step (8) is a command from the PC 70 to the optical power meter 210 tocommunicate received optical power in units of dB (instead of, forexample, watts).

Step (9) is a command from the PC 70 to the optical power meter 210defining a reference power level related to the difference between theoptical powers communicated to the receiver 40 and the optical powermeter 210, so that the optical power meter automatically communicatesthe power received by the receiver 40 to the PC 70.

Step (10) is a command from the PC 70 to the optical power meter 210instructing the optical power meter to trigger, i.e., to take an opticalpower reading and communicate this reading to the PC 70, upon receivinga command from the PC 70.

Step (11) is a command from the PC 70 to the electro-optic transducer160 to disable its output in order to perform the following step.

Step (12) displays a message on the PC 70 display requesting that theoperator connect the output of the electro-optic transducer 160 to thetransmitter optical splitter 260 input.

Step (13) is a command from the PC 70 to the electro-optic transducer160 to enable its output.

Step (14) is a command from the PC 70 to the oscilloscope 250 to employthe average mode, which means that the oscilloscope is to displaywaveforms consisting of points, each of which is the average of acurrent point and of a corresponding previous point, so as to smooth thewaveforms.

Step (15) is a command from the PC 70 to the oscilloscope 250 todetermine the upper and lower voltages of the electro-optic transducer160.

Step (16) determines the amplitude of the waveform and compares it tothe corresponding specification, e.g., greater than 0.00001 volts.

Step (17) calculates the extinction ratio of the electro-optictransducer using the equation:

    ER=(TOP LEVEL VOLTAGE)/(BOTTOM LEVEL VOLTAGE)

Step (18) compares the result of the calculation with the correspondingspecification to determine if the value should be saved, and displaysthe result.

With reference to Subroutine Q, which relates to the data dependentjitter calibration procedure, step (1) denotes that this portion of theprocedure relates to oscilloscope channel 256 and is the first of twoparts.

Step (2) denotes a command from the PC 70 to the switch control unit 150to set microwave switch 140 so that the output of serial patterngenerator 120 will be communicated to output port 144 and to set opticalswitch 200 so that the input to the optical switch 200 is via input port204.

Step (3) is a command from PC 70 to serial pattern generator 120 togenerate evenly spaced square waves at a transmission speed of interest,e.g., 200 Mb/s.

Step (4) is a command from the PC 70 to the oscilloscope 250 to employthe normal mode, i.e., the persist mode, in which new waveforms aresuperimposed on old waveforms so as to produce an eye pattern.

Step (5) is a command from PC 70 to the oscilloscope 250 specifyingreceiver channel range (in volts/division, e.g., 0.02 volts/division)and offset (the voltage corresponding to the center graticule of theoscilloscope, e.g., 0.0 volts).

Step (6) is a command from the PC 70 to the oscilloscope 250 to triggeron the leading edge of an input waveform, i.e., to display the waveformin response to the leading edge of the waveform.

Step (7) is a command from the PC 70 to the oscilloscope 250 in whichthe oscilloscope time base, i.e., nanoseconds/division (e.g., 10.0nanoseconds/division), and delay, i.e., the amount of time theoscilloscope should delay before initiating a waveform trace (e.g., 0.0nanosecond delay), are defined.

Step (8) displays a message on the PC 70 display requesting that theoperator connect a 10X probe from oscilloscope channel 256 to the pin onthe module socket 20 which corresponds to the transmitter non-invertinginput (I), and to connect a 10X probe from oscilloscope channel 255 tothe pin on the module socket 20 which corresponds to the transmitterinverting input (I-bar).

Step (9) is a command from the PC 70 to the oscilloscope 250 to employthe average mode, which means that the oscilloscope is to displaywaveforms consisting of points, each of which is the average of acurrent point and of a corresponding previous point, so as to smooth thewaveforms.

Step (10) is a command from the PC 70 to the oscilloscope 250 todetermine the upper and lower voltages of the electro-optic transducer160.

Step (11) determines the amplitude of the waveform and compares it tothe corresponding specification, e.g., greater than 0.04 volts.

Step (12) denotes a command from the PC 70 to the switch control unit150 to set microwave switch 140 so that the output of serial patterngenerator 120 will be communicated to output port 144 and to set opticalswitch 200 so that the input to the optical switch 200 is via input port204.

Step (13) is a command from the PC 70 to the serial pattern generator120 to generate the K28.5 pattern.

Step (14) is a command from the PC 70 to the oscilloscope 250 to employthe normal mode.

Step (15) is a command from the PC 70 to the oscilloscope 250 to triggerin response to clock pulses from the internal clock 130 of the serialpattern generator 120.

Step (16) is a command from the PC 70 to the oscilloscope 250 in whichthe oscilloscope time base, i.e., nanoseconds/division (e.g., 0.5nanoseconds/division), and delay, i.e., the amount of time theoscilloscope should delay before initiating a waveform trace (e.g., 0.0nanosecond delay), are defined.

Step (17) is a command from the PC 70 to the oscilloscope 250 in whichthe oscilloscope executes a built-in program to determine the jitterpresent in the waveform for channel 256. A command is then sent from thePC 70 to the oscilloscope 250 to return the value of measured jitter.

Step (18) compares the measured jitter result with the correspondingspecification and displays the result.

Step (19) repeats steps 2 through 17 using oscilloscope channel 255.

Step (20) compares the measured jitter result for channel 255 with thecorresponding specification to determine if the value should be savedand displays the result. The final data dependent jitter measurement isdetermined by taking the average jitter of the two channels.

With reference to Subroutine R, which relates to the duty cycledistortion calibration procedure, step (1) denotes a command from the PC70 to the switch control unit 150 to set microwave switch 140 so thatthe output of serial pattern generator 120 will be communicated tooutput port 144 and to set optical switch 200 so that the input to theoptical switch 200 is via input port 204.

Step (2) is a command from PC 70 to serial pattern generator 120 togenerate evenly spaced square waves at a transmission speed of interest,e.g., 200 Mb/s.

Step (3) is a command from the PC 70 to the oscilloscope 250 to employthe normal mode, i.e., the persist mode, in which new waveforms aresuperimposed on old waveforms so as to produce an eye pattern.

Step (4) is a command from PC 70 to the oscilloscope 250 specifyingreceiver channel range (in volts/division, e.g., 0.02 volts/division)and offset (the voltage corresponding to the center graticule of theoscilloscope, e.g., 0.0 volts).

Step (5) is a command from the PC 70 to the oscilloscope 250 to triggeron the leading edge of an input waveform, i.e., to display the waveformin response to the leading edge of the waveform.

Step (6) is a command from the PC 70 to the oscilloscope 250 in whichthe oscilloscope time base, i.e., nanoseconds/division (e.g., 2.0nanoseconds/division), and delay, i.e., the amount of time theoscilloscope should delay before initiating a waveform trace (e.g., -4.4nanosecond delay), are defined.

Step (7) displays a message on the PC 70 display requesting that theoperator connect a 10X probe from oscilloscope channel 256 to the pin onthe module socket 20 which corresponds to the transmitter non-invertinginput (I), and to connect a 10X probe from oscilloscope channel 255 tothe pin on the module socket 20 which corresponds to the transmitterinverting input (I-bar).

Step (8) is a command from the PC 70 to the oscilloscope 250 to employthe average mode, which means that the oscilloscope is to displaywaveforms consisting of points, each of which is the average of acurrent point and of a corresponding previous point, so as to smooth thewaveforms.

Step (9) is a command from the PC 70 to the oscilloscope 250 todetermine the upper and lower voltages of the transmitter input signalI.

Step (10) determines the amplitude of the waveform and compares it tothe corresponding specification, e.g., greater than 0.04 volts.

Step (11) is a command from the PC 70 to the oscilloscope 250 to employthe average mode.

Step (12) is a command from the PC 70 to the oscilloscope 250 to triggeron the leading edge of an input waveform.

Step (13) is a command from the PC 70 to the oscilloscope 250 todetermine the upper and lower voltages of the transmitter input signalI-bar.

Step (14) determines the amplitude of the waveform and compares it tothe corresponding specification, e.g., greater than 0.04 volts.

Step (15) is a command from the PC 70 to the oscilloscope 250 tosubtract the two channels I minus I-bar.

Step (16) is a command from PC 70 to the oscilloscope 250 specifyingreceiver channel range (in volts/division, e.g., 0.05 volts/division)and offset (the voltage corresponding to the center graticule of theoscilloscope, e.g., 0.0 volts).

Step (17) is a command from the PC 70 to the oscilloscope 250 to employthe average mode.

Step (18) involves a series of commands from the PC 70 to theoscilloscope 250 to measure the positive and negative widths of thewaveform. Step (18a) is a command from the PC 70 to the oscilloscope 250to measure the time between the first rising edge and the first fallingedge of the waveform. If the result of this measurement is a positivevalue (step 18b), then measure the time between the first falling edgeand the second rising edge (step 18c) to obtain the negative width. Ifthe result of step 18a was a negative value (step 18d), then measure thetime between the first rising edge and the second falling edge (step18e) to obtain the positive width.

Step (19) calculates the duty cycle distortion from the equation:

    duty cycle distortion=((positive width)-(negative width))/2.0

Compare the value of duty cycle distortion with the correspondingspecification to determine if the value should be saved and displays theresult.

SUBROUTINE A

Receiver Sensitivity

1) Set DUT voltage for the measurements

2) Set switches for receiver measurement

3) Set BER transmitter for square wave

4) Set scope to receiver channels

5) Set receiver channel range and offset

6) Trigger on waveform

7) Set Scope Time Base and Delay

8) Set scope to acquire average mode--2 averages

9) Get the lower and upper receiver waveform voltages

10) Set switches for receiver measurement with CLOCK1 sync

11) Set BER transmitter for pseudo random pattern

12) Set BER receiver for pseudo random pattern

13) Set scope to acquire normal mode

14) Trigger on BER clock

15) Set Receiver Threshold to O.O volts

16) Set power meter units for dB

17) Set power meter reference for receiver measurement

18) Set power meter trigger for triggered mode

19) Measure Window width and power setting--Center is in RxWindowCen

19a) Set Measure Period

19b) Set Delay Generator

19c) Set Receiver Estimated Laser power output level

19d) Decrement power until receiver threshold is found

19e) Gets the size of the window

19e-1) Set Measure Period

19e-2) Set Delay Generator to estimated upper edge of window

19e-3) Increment delay until errors occur

19e-4) Set Delay Generator to estimated lower edge of window

19e-5) Decrement delay until errors occur

19e-6) Save the delay times

19f) Calculate and save size of window and center of window

20) Set delay to -0.7 ns from center of window

21) Adjust power level for BER between 1E-7 and 1E-8

21a) Set Measure Period for 1 second

21b) Do coarse adjustment

21c) Check bit error rate

21d) Get second bit error rate

21e) Check bit error rate

21f) Estimate power level for desired bit error rate

21g) Do fine adjustment

22) Determine the 3 power levels to-use

23) Save power levels for +-0.7 ns tests

24) Set Measure Period for 2 seconds

25) Measure Bit Error Rate for all three power levels

26) Calculate best fit and extrapolate to BER 1E-15

27) Add the penalty for not using 4:1 extinction ratio

28) Get Correlation and slope values

29) Check Sensitivity for PASSED/FAILED

30) Set delay to +0.7 ns from center of window

31) Adjust power level for BER between 1E-7 and 1E-8

31a) Set Measure Period for 1 second

31b) Do coarse adjustment

31c) Check bit error rate

31d) Get second bit error rate

31e) Check bit error rate

31f) Estimate power level for desired bit error rate

31g) Do fine adjustment

32) Determine the 3 power levels to use

33) Set Measure Period for 2 seconds

4) Measure Bit Error Rate for all three power levels

35) Calculate best fit and extrapolate to BER 1E-15

36) Add the penalty for not using 4:1 extinction ratio

37) Get Correlation and slope values

38) Check Sensitivity for PASSED/FAILED

SUBROUTINE B

Receiver Pulse Width Distortion

1) Set DUT voltage for the PWD measurement

2) Set switches for receiver measurement

3) Switch BER transmitter to square wave pattern

4) Set scope to receiver channels

5) Set receiver channels range and offset (DC couple)

6) Trigger on waveform

7) Set Scope Time Base and Delay

8) Set power meteor units for dB

9) Set power meter reference for receiver measurement

10) Set power meter trigger for triggered mode

11) Set receiver power level

12) Set scope to acquire average mode--16 averages

13) Measure top and bottom of waveform

14) Check for sufficient amplitude

15) Get positive end negative widths of waveform in nanoseconds

15a) Get first pulse

15b) Check if positive width

15c) Get negative width

15d) Check if negative width

15e) Get positive width

16) Calculate Pulse Width Distortion percent

SUBROUTINE C

Receiver Signal Detect Threshold

1) Set DUT supply voltage

2) Set switches for receiver measurement

3) Set BER transmitter for pseudo random pattern

4) Set power meter units for dB

5) Set power meter reference for receiver measurement

6) Set power meter trigger for triggered mode

7) Find the Receiver Signal Detect Threshold

7a) Decrease power until Signal Detect indicates no signal is beingdetected

8) Save/Receiver Signal Detect Threshold

9) Add the penalty for not using 4:1 extinction ratio

10) Check Receiver Signal Detect Threshold power for PASSED/FAILED

SUBROUTINE D

Receiver Signal Detect Assert/Deassert Times

1) Set DUT supply voltage

2) Set switches for receiver measurement with Gate sync

3) Turn on BERT gate input

4) Set Gate Input channel range, offset, and coupling

5) Set signal Detect channel range, offset, and coupling

6) Set scope Trigger for gate channel

7) Set Scope Time Base and Delay

8) Set power meter units for dB

9) Set Optical Power Meter Reference for Receiver

10) Set Power meter trigger for triggered mode

11) Set power level

12) Set scope to average mode with 2 channels--32 averages

13) Get the lower and upper Gate Input waveform voltages

14) Get the lower and upper Signal Detect waveform voltages

15) Get times of first positive edges

16) Convert to microseconds and save

17) Check Receiver Signal Detect Assert Time for PASSED/FAILED

18) Get times of first negative edges

19) Convert to microseconds and save

20) Check Receiver Signal Detect Deassert Time for PASSED/FAILED

SUBROUTINE E

Transmitter Average Power

1) Set DUT supply voltage

2) Set switches for transmitter measurement with CLOCK1 sync

3) Set BER transmitter for pseudo-random pattern

4) Set power meter units for dB

5) Set power meter reference for transmitter measurement

6) Set power meter trigger for continuous

7) Measure Average Power

8) Check for dead transmitter

9) Check Average Power for PASSED/FAILED

SUBROUTINE F

Transmitter Rise/Fall Time

1) Set DUT supply voltage

2) Set switches for transmitter measurement

3) Switch serial test pattern generator to Square Wave

4) Set transmitter channel ranger offset, and coupling

5) Trigger on waveform

6) Set Scope Time Base and Delay

7) Set scope to acquire average mode--4 averages

8) Measure peak amplitude of waveform

9) Check for sufficient amplitude

10) Measure baseline and topline of waveform

11) Measure Rise Time between 20% and 80% values

12) Check Rise time for PASSED/FAILED

13) Measure Fall Time using rise time voltage values

14) Check Fall time for PASSED/FAILED

SUBROUTINE G

Transmitter Extinction Ratio

1) Set DUT supply voltage

2) Set switches for transmitter measurement

3) Set BER transmitter for square wave pattern

4) Set transmitter channel ranger offset, and coupling

5) Trigger on waveform

6) Set Scope Time Base and Delay

7) Set scope to average mode--4 averages

8) Measure peak amplitude of waveform

9) Check for sufficient amplitude

10) Measure baseline and topline of waveform

11) Calculate extinction ratio

12) Check Extinction Ratio for PASSED/FAILED

SUBROUTINE H

Transmitter Duty Cycle Distortion

1) Set DUT supply voltage

2) Set switches for transmitter measurement

3) Switch BER transmitter to square wave pattern

4) Set transmitter channel range, offset, and coupling

5) Trigger on waveform

6) Set Scope Time Base and Delay

7) Set scope to acquire average mode--8 averages

8) Measure top and bottom of waveform

9) Check for sufficient amplitude

10) Use 50% point of 0.0. AC coupled

11) Get positive and negative widths of waveform in nanoseconds

11a) Get first pulse width

11b) If positive width

11b-1) Get negative width

11c) If negative width

11c-1) Get positive width

12) Calculate Duty Cycle Distortion in picoseconds and check results

SUBROUTINE I

Transmitter Data Dependent Jitter

1) Set DUT supply voltage

2) Set switches for transmitter measurement

3) Switch BER transmitter to square wave pattern

4) Set Scope Time Base and Delay

5) Set transmitter channel range, offset, and coupling

6) Trigger on waveform

7) Set scope to acquire average mode--2 averages

8) Measure top and bottom of waveform

9) Check for sufficient amplitude

10) Switch serial test pattern to K28.5 (Data Dependent Jitter Pattern)

11) Set scope to normal acquisition

12) Set Scope Trigger offset and slope

13) Use scope jitter routine to obtain jitter

13a) Set scope to display to color graded

13b) Set absolute ranges

13c) Set left and right zones

13d) Measure top and bottom of waveform

13e) Loop until the number of points is equal to or greater than desired

13f) Get jitter measurement

13g) Convert to picoseconds

14) Check jitter results

SUBROUTINE J

Optical Power Meter Calibration

1) Initialize the Optical Power Meter for Calibration

2) Insert just the optical head calibration factor

3) Set power meter wavelength

4) Get the Floor Reference Power Meter reading

5) Get the Power Meter reading of the Floor Reference Power

6) Calculate power Delta

7) Insert new meter calibration factor

8) Re-measure Reference Power on the Power Meter

9) If measurement PASSED, save the new meter correction factor

SUBROUTINE K

Transmitter Fixture Calibration

1) Initialize meter with calibration factor

2) Set power meter trigger for continuous

3) Set meter reference to 0.0

4) Set power meter wavelength

5) Measure the Floor Reference Power through the Transmitter ReferenceCable

6) Calculate the Transmitter Fixture/Fiber Loss

7) Display results

SUBROUTINE L

Transmitter Link Calibration

1) Set optical switches to read Transmitter link power

2) Initialize meter with calibration factor

3) Set power meter trigger for continuous

4) Set meter reference to 0.0

5) Set power meter wavelength

6) Measure the Floor Reference Power through the Tx Fixture/Fiber andLink

7) Calculate Transmitter Link Delta and Loss

8) Set new Transmitter Reference

9) Measure the Floor Reference Power through the Tx Reference Cable andTx Link with the reference set

10) If measurement PASSED, save the new Tx Link Loss

SUBROUTINE M

Receiver Link Calibration

1) Set switches for receiver measurement

2) Initialize meter with calibration factor

3) Set power meter trigger for continuous

4) Set meter reference to 0.0

5) Set power meter wavelength

6) Set attenuator to 0.0

7) Measure laser power out of receiver duplex connector

8) Measure Laser Power of 10% leg of splitter

9) Calculate the difference

10) Set the Power Meter Reference to the difference

11) Measure Laser Power to DUT Receiver through splitter with referenceset

12) If measurement PASSED, save the new Rx Link Loss

SUBROUTINE N

Frequency Generator Calibration

1) Determine minimum and maximum limits

2) Set switches for transmitter measurement

3) Set scope to acquire normal mode for initialization

4) Set channel range, offset, and coupling

5) Trigger on channel

6) Set Scope Time Base and Delay

7) Set scope to acquire average mode--4 averages

8) Prompt operator to connect frequency generator to scope

9) Loop on calibration information

9a) Check frequency

9b) Check amplitude

9c) Check offset

9d) Check keyboard termination character

SUBROUTINE O

Oscilloscope Calibration

1) Calibrate channel L1 O/E converter

2) Calibrate channel C1

3) Calibrate channel C2

4) Calibrate channel R1

5) Calibrate channel R2

6) Display calibration result

SUBROUTINE P

Laser Source Extinction Ratio Calibration

1) Set switches for transmitter measurement

2) Set Anristu to drive LASER source

3) Set BER transmitter for 100 MHz square wave

4) Set scope to acquire normal mode

5) Set transmitter channel range and offset

6) Trigger on waveform

7) Set Scope Time Base and Delay

8) Set power meter units for dB

9) Set power meter reference for receiver measurement

10) Set power meter trigger for continuous mode

11) Ensure LASER is off

12) Prompt operator to make fiber connections

13) Turn LASER source on

14) Set scope to acquire average mode--32 averages

15) Measure amplitude of waveform

16) Check for sufficient amplitude

17) Calculate extinction ratio

18) Display Extinction Ratio results

SUBROUTINE Q

Data Dependent Jitter Calibration

1) First part of DDJ Cal using Channel C1

2) Set switches for transmitter measurement

3) Switch BER transmitter to square wave pattern

4) Set scope to normal acquisition while being initialized

5) Set channel range, offset, and coupling

6) Trigger on BER clock

7) Set Scope Time Base and Delay

8) Prompt operator to make probe connections

9) Set scope to acquire average mode--4 average

10) Measure top and bottom of waveform

11) Check for sufficient amplitude

12) Set switches for transmitter measurement with CLOCK1 sync

13) Switch serial test pattern to K28.5 (Data Dependent Jitter Pattern)

14) Set scope to normal acquisition

15) Set Scope Trigger offset and slope for CLOCK1 Sync

16) Set Scope Time Base and Delay

17) Use scope jitter routine to obtain jitter

18) Check jitter results

19) Repeat using Channel C2

20) Check return code and display results

SUBROUTINE R

Duty Cycle Distortion Calibration

1) Set switches for transmitter measurement

2) Switch BER transmitter to square wave pattern

3) Set scope channel to normal acquisition while being initialized

4) Set channel range, offset, and coupling

5) Trigger on waveform

6) Set Scope Time Base and Delay

7) Prompt operator to make probe connections

8) Set channel to test amplitude--4 averages

9) Measure top and bottom of waveform

10) Check for sufficient amplitude

11) Set channel to test amplitude--4 averages

12) Trigger on waveform

13) Measure top and bottom of waveform

14) Check for sufficient amplitude

15) Set scope subtract function

16) Set channel range, offset, and coupling

17) Set scope to acquire average mode--16 averages.

18) Get positive and negative widths of waveform in nanoseconds

18a) Get first pulse

18b) Check if positive width

18c) Get negative width

18d) Check if negative width

18e) Get positive width

19) Calculate Duty Cycle Distortion in picoseconds and check result

We claim:
 1. A method for testing an electro-optic module which includesan electro-optic receiver, comprising the steps of:providing anautomated test system for testing electro-optic modules which includeelectro-optic receivers; connecting an electro-optic module whichincludes an electro-optic receiver to said automated test system; andautomatically measuring a receiver sensitivity associated with saidelectro-optic receiver, which receiver sensitivity is defined as theaverage optical power (P) of the weakest digital optical signaldetectable by said electro-optic receiver at a specified bit error rate(BER).
 2. The method of claim 1, wherein said step of automaticallymeasuring said receiver sensitivity at said specified BER includes thestep of measuring three BERs, different from said specified BER,corresponding to three different measured values of P.
 3. The method ofclaim 2, wherein said step of automatically measuring said receiversensitivity at said specified BER includes the step of calculating threevalues of a signal-to-noise parameter, Q, associated with saidelectro-optic receiver, corresponding to said three measured BERs andthe three measured values of P.
 4. The method of claim 3, wherein saidstep of automatically measuring said receiver sensitivity at saidspecified BER includes the step of fitting a linear-least-squares-fitapproximation to three data points represented by said three calculatedvalues of Q and the three corresponding, measured values of P.
 5. Themethod of claim 4, wherein said step of automatically measuring saidreceiver sensitivity at said specified BER includes the step ofcalculating a value of Q corresponding to said specified BER.
 6. Themethod of claim 5, wherein said step of automatically measuring saidreceiver sensitivity at said specified BER includes the step ofextrapolating said linear-least-squares-fit approximation to saidcalculated value of Q corresponding to said specified BER, to therebydetermine the value of P corresponding to said specified BER.
 7. Themethod of claim 1, wherein said automated test system includes anelectro-optic transducer which exhibits a first extinction ratio, LSER1,and wherein said automatically measured receiver sensitivity correspondsto said first extinction ratio, LSER1.
 8. The method of claim 7, whereinsaid step of automatically measuring said receiver sensitivity includesthe step of calculating receiver sensitivity corresponding to a secondextinction ratio, LSER2, said calculating step including the step ofadding a correction factor, CR, to said automatically measured receiversensitivity corresponding to said first extinction ratio, LSER1, saidcorrection factor, CR, being given by

    CR=10* log ((LSER2+1)/(LSER2-1)) -10* log ((LSER1+1)/(LSER1-1)).